Question

i found this function that validates the length of twitter account.

Your username can contain up to 15 characters.

function validate_username($username)
{
    return preg_match('/^[A-Za-z0-9_]{1,15}$/', $username);
}

How can I change this rule to make @ symbol optional in the beginning of the string !

Samples of valid inputs

abcdabcdabcdabc

@abcdabcdabcdabc

Answer 1

The ? can be used to to make the previous character optional:

preg_match('/^@?[A-Za-z0-9_]{1,15}$/', $username);

Equivalently:

preg_match('/^@{0,1}[A-Za-z0-9_]{1,15}$/', $username);